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Name: ________________________________ ID# ______________________ Date Submitted: __________________ Lab Section # ____________________ CSE 2441 – Introduction to Digital Logic Spring Semester 2013 Lab Number 4 -- A Simple Arithmetic Unit (Due by 5:00 PM on February 22, 2013) CSE 2441 LABORATORY SESSION 4 SPRING 2013 A SIMPLE ARITHMETIC UNIT (100 POINTS) PURPOSE/OUTCOMES: To design, implement, and test a simple two-function arithmetic unit. By successfully completing this laboratory, you will have demonstrated an ability to design combinational logic circuits and an understanding of 2’s-complement numbers and arithmetic. BACKGROUND: In Lab Session 3, you constructed a four-bit adder and a four-bit subtractor using an SN7483 IC as the basic component. In this lab, you will use the knowledge gained in that exercise to design, verify, construct, and test a four-bit arithmetic unit (AU) that can add or subtract and detect overflow conditions. The block diagram for the AU is shown below. A4 A3 A2 A1 B4 B3 B2 B1 OVR Arithmetic Unit (AU) AddSub (Add=0, Sub=1) Cout R4 R3 R2 R1 If AddSub = 0, then R = A + B. If AddSub = 1, then R = A – B. Cout = the carry-out produced by either the + or – operation. OVR = 1 will indicate that an overflow condition resulted from the + or – operation. OVR = 0 when there was no overflow. Negative numbers are to be represented by 2’s complement. PRELAB (25 points): 1. Design an adder/subtractor for the AU that meets the above specifications. Use one SN7483 as the basic component of the design. Use XOR2 gates to perform the bitwise complement of input B as needed for addition or subtraction. Capture and verify your design using QuartusII/Qsim. Refer to section 4.8 of Nelson, Nagle, Carroll, and Irwin for more information. 2. Design a combinational logic circuit for detecting arithmetic overflow in the above AU. Capture and verify your design using QuartusII/Qsim. LAB WORK (Have the lab instructor check your work after each part.) Part 1 (50 Points): Construct the 4-bit adder-subtractor section of your ALU. Test the adder/subtractor with the following additions and subtractions. Record your results. Then examine and explain each result. 3+4=? 6+6=? 7-5=? 7–1=? 7+1=? 5 - (-4) = ? (-2) + (-4) = ? (-2) - (-4) = ? (-4) - (-2) = ? (-5) - 6 = ? (-5) - (-5) = ? 5–5=? Part 2 (25 Points): Construct and integrate your overflow detector circuit with the adder-subtractor that you built above. Test the overflow circuit with the same input patterns given in part 1 and record your results.